1. Field
Embodiments relate to a cap assembly and a secondary battery having the same and, more particularly, to a cap assembly having a stable connection between a safety vent and a cap-up thereof, without increasing a thickness of an end of the cap assembly, and a secondary battery having the same.
2. Description of the Related Art
In recent times, compact, slim, and light-weight portable electric/electronic devices, e.g., cellular phones, notebook computers, and camcorders, are actively developed and produced. These devices include a battery pack that is used in places where a power source is not provided. Examples of the battery pack include nickel-cadmium (Ni—Cd), nickel-metal hydride (Ni-MH) and lithium (Li) batteries. In consideration of economic feasibility, the battery pack may generally be a secondary battery, which can be recharged.
The lithium secondary battery is widely used for the portable electric/electronic devices because of the advantages that the lithium second battery has over both the nickel-cadmium battery and the nickel-metal hydride battery. For example, the lithium secondary battery has an operational voltage about three times larger than that of the nickel-cadmium battery or the nickel-metal hydride battery. Also, the lithium secondary battery has a higher energy density per unit weight than the nickel-cadmium and the nickel-metal hydride batteries. The lithium secondary battery may be classified based on the kind of electrolyte, e.g., a lithium ion battery using a liquid electrolyte or a lithium polymer battery using a polymer electrolyte. The lithium secondary battery may be also classified based on the shape thereof, e.g., cylindrical, prismatic or pouch type.
The secondary battery generally includes an electrode assembly, a can housing the electrode assembly and an electrolyte allowing migration of lithium ions in the electrode assembly, and a cap assembly sealing the can. The electrode assembly includes a positive electrode plate having a positive electrode collector to which a positive electrode active material is applied and a positive electrode tab electrically connected to a side of the positive electrode assembly. The electrode assembly further includes a negative electrode plate having a negative electrode collector to which a negative electrode active material is applied and a negative electrode tab electrically connected to a side of the negative electrode collector. A separator is included in the electrode assembly to interpose between the two electrode plates.
The cap assembly of a cylindrical secondary battery is a bit different from other types, i.e., prismatic or pouch type of the lithium secondary battery. The cap assembly of a cylindrical secondary battery generally includes a cap-up and a safety vent. The cap-up may be electrically connected to an external terminal and to a top opening of the can to seal the can, and a safety vent may be electrically connected to the positive or negative electrode plate and may deform or break in order to discharge gas outside when an inner pressure of a cylindrical secondary battery is higher than a predetermined level due to gas generated from the electrode assembly. The cap assembly may further include a current interrupt device (CID) disposed on the safety vent. The CID may be deformed or broken by the safety vent to interrupt an electrical connection between the electrode assembly and an external terminal when the safety vent is deformed or broken due to the internal gas. The cap assembly may further include a positive temperature coefficient (PTC) thermistor disposed between the CID and the cap-up, or between the safety vent and the CID to prevent overcurrent between the electrode assembly and the external terminal.